The present invention relates to an open end spinning device and, more particularly, to an open end spinning device which has a spinning rotor which is driven at speeds of between 50,000 and 70,000 rp.m.s. for producing yarns having a low limiting twist coefficient.
It is known that open-end yarns must be twisted harder than ring-spun yarns and, consequently, exhibit a harder feel (Melliand-Textilberichte 2/52 (1971), pages 127-132). For many purposes, e.g., for knitwear and hosiery, ring-spun yarns are for that reason preferred to open-end yarns, In order to broaden the field of use of open-end yarns it is therefore necessary to reduce the twist in the yarn. A reduction in the twist means a low twist coefficient .alpha.. But at the same time an increase in production is thereby achieved through increased thread draw-off speed at the same rotational speed of the rotor (Melliand Textilberichte 2/1975, pages 98-104).
It is further known that by increasing the false twist effect, the limiting twist coefficient .alpha..sub.min can be reduced. For this purpose, thread draw-off tube mouths have become known, which are provided with grooves or ribs (West German A/S 1 560 302, and U.S. Pat. Nos. 3,640,061 and 3,805,505. But these mouths cause roughening of the thread and for that reason cannot be used arbitrarily.